“I’ll buy in California and sell to New Yorkers,” says Chuck, the robotic voice that represents a California dealer that has moved east. The Planet Money story portrays this black market sale as something a bit new, a reaction to dropping prices on the West Coast.

Dealers aren’t the only ones with an incentive to move marijuana out of California. The legalization of medical marijuana led to a rush of pot farmers with permits to grow marijuana legally. That in turn led to a supply glut — and plummeting wholesale prices. Some growers haven’t been able to unload all their crops at the price they want on the local, legal market. So they break the law and send it out of state.

Of course, the movement of cannabis out of Humboldt and to states on the east side of the country has been going on for decades. Nonetheless, the story is good and offers a simple explanation of the marijuana economy and how law enforcement plays a part in keeping prices up.